ZoBell — 204 — Marine Microbiology 



When suspended in brine from the lake, most sewage or fresh-water bac- 

 teria were killed within a few minutes. 



The Dead Sea : — The salt composition of Dead Sea water is distin- 

 guished from that of other naturally occurring brines by the predominance 

 of magnesium chloride and the relative abundance of bromides. The 

 total salt content ranges from 227 to 330 grams per liter. Although this 

 body of water has the popular reputation of being lifeless, Elazari- 

 VoLCANi (1940) found numerous bacteria in water and mud samples. He 

 reports the presence of several species of algae, including genera of Chloro- 

 phyceae, Diatomeae, and Cyanophyceae. 



Elazari-Volcani isolated organisms similar to Micrococcus morrhuae, 

 Bacterium trapanicum, Bacterium halobitim, Pseudomonas indigofera, and 

 Sarcina morrhuae from the Dead Sea. Flavohacterium maris-mortui, 

 Chromohacterium maris-mortui, Pseudomonas halestorgus, and Flavohac- 

 terium halmephilum were described as new species. The organisms 

 thrived in media containing from 3 to 30 per cent salt. Organisms carried 

 into the Dead Sea by inflowing streams failed to grow in the saline waters, 

 but certain terrigenous spore formers exhibited remarkable salt resistance. 



In bottom sediments of the Dead Sea, Elazari-Volcani (1943) dem- 

 onstrated the presence of cellulose decomposers, hydrocarbon oxidizers, 

 denitrifiers, and sulfur bacteria. He found both aerobes and anaerobes in 

 stratified cores. Some of the latter were 170 cm. long and were collected 

 from water depths of 70 to 330 meters. The bacteria developed in enrich- 

 ment media containing 25 per cent salt. 



Fresh-water lakes: — The factors which influence the distribution 

 and activities of bacteria in fresh-water lakes have been discussed in the 

 preceding chapters. The parts played by bacteria and aflied microorgan- 

 isms in lakes as producers of plant nutrients, in the cycle of elements, as 

 geological agents, in the food cycles of animals, as agents which influence 

 physico-chemical conditions, as parasites, and in their relations to higher 

 organisms are analogous to those features of marine bacteria, to which 

 frequent references have already been made. 



Although most hydrobiologists and limnologists recognize that bac- 

 teria play an important part in the economy of lakes ; hydrobacteriology 

 of lakes, like that of the sea, has lagged considerably behind other biolog- 

 ical sciences in participating in the study of lake metabolism and ecology. 

 Whereas zoologists and botanists have classified their organisms as to 

 species, habitat, and activity, bacteriologists have only the most general 

 ideas regarding the characteristics, distribution, and activities of bacteria 

 which live normally in lake water and bottom deposits. Until a decade 

 ago the emphasis had been placed upon the occurrence of bacteria of sani- 

 tary significance in lakes (Minder, 1920). 



The fragmentary literature on the subject suggests that the micro- 

 flora of lakes differs qualitatively from that of the surrounding soil and 

 inflowing streams. For example. Snow and Fred (1926) noted that 

 nearly half of the bacteria isolated from Lake Mendota, Wisconsin, were 

 brilliantly pigmented, whereas fewer than ten per cent of the known spe- 

 cies of soil bacteria are chromogenic. Regarding the characteristics of 

 bacteria in Lake Mendota, they write: 



"The bacteria of lake water, taken far out from shore, show certain 

 well defined characteristics. The kind of microorganisms present in the 



